Work will be continued on the association between axoplasmic microtubules, and membrane-limited structures. In previous work, we described limkage between microtubules and synaptic vesicles and more recently investigated microtubule-mitochondrion distribution by comparison between electron micrographs and computed axon 'models'. The cross-bridging of microtubules and mitochondria is a new aspect of axoplasmic organization, and will be under continued study during the proposed grant period. High resolution observations on cross-bridges and on the disruption induced by Vinca alkaloids will be carried out. Computer analysis of axoplasmic architecture and notably of multiple association between mitochondria and microtubles, will be extended. Studies on thin sectioned material will be augmented by work on carbon-platinum replicas of freeze-fractured axons. Factors involved in the linkage between synaptic vesicles and microtubules in near central and peripheral synaptic foci will be investigated in invertebrate material. Freeze-fracture replication will also be used in continuing studies on the structure of membranes of physiologically and pharmacologically distinct muscles; in particular, in cholinergic and non-cholinergic fibers. BIBLIOGRAPHIC REFERENCES: Smith, D.S., Jarlfors, Ulla and Cameron, Bruce F. (1975) Morphological evidence for the participation of microtubules in axonal transport. Ann. N.Y. Acad. Sci. 253, 472-506. Smith D.S., Baerwald, R.J., and Hart, M.A. (1975) The distribution of otheogonal assemblies and other intercalated particles in frog sartorius and rabbit sacrospinalis muscle. Tissue & Cell, 7, 369-382.